The present invention is directed to a quick-release locking device for selectively locking and unlocking a first telescoping member to a second telescoping member, and in particular to a locking device which prevents movement of the first telescoping member in both a first longitudinal direction and a second and opposite longitudinal direction with respect to the second telescoping member while selectively permitting longitudinal movement of the first telescoping member in either the first or second longitudinal direction.
Prism poles are used in surveying to support surveying equipment such as a prism at a desired height above ground level while facing in a desired direction. Prism poles typically include a plurality of telescoping poles or tubes located concentrically one within the other to provide for selective height adjustment. The outermost tube includes a lower end which engages the ground and the innermost tube includes an upper end having a mounting mechanism for attaching a piece of surveying equipment such as a prism thereto. The inner tube is slidable along its central longitudinal axis in a first longitudinal direction or in a second and opposite longitudinal direction such that the distance between the lower end of the prism pole and the upper end of the prism pole may be varied as required. While a prism pole is preferably selectively adjustable in length, the telescoping members of the prism pole preferably should be capable of being selectively locked to one another such that the upper end of the prism pole will not move relative to the lower end of the prism pole once a height for the prism is selected. A locking device is therefore required to selectively lock an inner telescoping member to an outer telescoping member while selectively allowing sliding longitudinal movement therebetween. In addition to providing selective locking and unlocking of an inner telescoping member to an outer telescoping member, the locking device should also include a quick-release feature to allow the quick and easy adjustment of the overall length of the prism pole. The locking device of the present invention provides these features.